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An ambulance passes you at a speed of 15.0m/s . If its siren has a frequency...

An ambulance passes you at a speed of 15.0m/s . If its siren has a frequency of 995 Hz what is difference in the frequencies you perceive before and after it passes you? (Assume the speed of sound in air is 331 m/s.)

(Correct answer is 90.0 Hz but I'm getting 128.6 Hz)

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Answer #1

where ƒ = observed frequency

c = speed of sound

Vs = velocity of source (negative if it’s moving toward the observer)

ƒ0 = emitted frequency of source

When ambulance is approaching :

When ambulance has passed :

Hence difference = 1042.23 - 951.86 = 90.37 Hz 90 Hz

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